Help regarding Recap Exercise 3 lucas_number

I have successfully done the first question multiply(a,b), now How to tackle lucas_number(num) ? It asks to be solved recursively. What I have done is that I wrote a helper function which gives a n-th lucas number, This is done recursively. In the main method I have used a loop to append the n-th lucas values to an array. Is my approach correct? Is this the correct way to do this. If needed I will post my whole solution too.